HTML and CSS Style Guide by Google

Google introduced to this new style guide. This code makes more effective, efficient, maintainable and elegant. When we working on HTML/CSS code with several developers and many teams or any companies, this code helps to be consistent and easy to understand.

HTML / CSS Style Contents :

General Style Rules	Protocol
General Formatting Rules	Indentation Capitalization Trailing whitespace
General Meta Rules	Encoding Comments Action items
HTML Style Rules	Document type HTML validity Semantics Multimedia fallback Separation of concerns Entity references Optional tags type attributes
HTML Formatting Rules	General formatting
CSS Style Rules	CSS validity ID and class naming ID and class name style Type selectorsShorthand properties 0 and units Leading 0s Quotation marks in URI values Hexadecimal notation Prefixes ID and class name delimiters Hacks
CSS Formatting Rules	Declaration order Block content indentation Declaration stops Property name stops Selector and declaration separation Rule separation
CSS Meta Rules	Section comments

Source : http://google-styleguide.googlecode.com/svn/trunk/htmlcssguide.xml